Photographic exposure meter



Oct. 8, 1940.

W. SCHAFER PHOTOGRAPHIC EXPOSURE METER Filed July l, 1938 2 Sheets-Sheetl INVENTOR ATTO Patented Oct. 8, 1940 UNITED STATES PATENT OFFICE '2PHOTOGRAPHIC EXPOSURE METER Willy .Schaf er, Wetzlar, Germany, assignor,by

mesne assignments, to

Switzerland Frank Dumur, Lausanne,

Application July l, 1938, Serial N6. 216,880

In Germany Julyfi, 1937 3 Claims.

are used to equal the light intensity in the fields of light from theobjective and-from the standard light for purposes of comparison.

The object of the invention is to provide -an exposure meter of verysimple novel construction and one which will not occupy much space.

With'this object in viewthe invention is embodied in an exposure meterwhich includes two disk formed neutral wedges which are supported on acommon shaft. The light weakening or light gradating property of eachwedge runs in opposite directions. The optical arrangementis such thatthe neutral wedges are supported to move in or adjacent to the two lightentrance pupils which are preferablyof the same size.

In the accompanying drawings Fig. l is a diagram illustrating thearrangement of the main optical elements in'the exposure meter. I

Fig. 2 is a rear view of the exposure meter in operative position upon acamera with parts in section and parts brokenaway.

Fig. 3 is a view of the scale rings of the exposure meter. a

Fig. 4 is a plan view of the exposure meter with parts in section andparts broken away.

Referring first toFig- 1 the numeral I indicates an operating shaft uponwhich two disk formed neutral wedges 2 and 3 are mounted for operationas will be hereinafter described. As indicated in the drawings thedensity of the disk 2 is greatest at A and decreases in a clockwisedirection, whereas the density of the disk 3 isgreatest at B anddecreases in anti-clockwise direction. The objective 4 and the ocular 5to-' gether with the prisms 6, l, and 8 form a telescopic View finder,the arrangement being such that the image is observed erect and with theright and left sides thereof in proper position.

The standard light is indicated at 9 in the form of an electric lampfrom whichjthe light rays pass through the entrance pupil at M, whichlies in the disk 3 and then through the prisms l and II to the partlysilvered surface l2 in which said rays are united with the light raysfrom the object which come in through the objective 4 and pass throughthe prism 6, then through the entrance pupil l3, which lies in the disk2 then through the prisms l and 8 and then join the rays from the lamp'in the said-silvered surface [2.

to the ocular 5. It will be seen that by rotating the shaft l the lightfrom the object is weakened or strengthened and to the sameextent thelamp light is strengthened or weakened according to the direction ofrotation. The ,c0rrect exposure.

is indicated when the two bundles of light rays reach the same degree ofintensity.

The aforesaid optical elements maybe embodied in an exposure meterof thetype similar to that shown in my pending application Serial No. 204,965filed April 29, 1938, as shown in Figs.

2, 3 and 4. Referring to the latter the'reference' numeral 55 denotes amodern miniature hand camera of a well known type. j The' camera is"provided with the usual shutter setting knob 56 having a transverseslot 51. The camera also has an undercut recess 58 for the reception ofa foot 59 on the bottom of the exposure meter casing 60. Within thelatter the elements shown in Fig. 1 are arranged so as to. be operablein connection with the shutter of the camera.

The shaft l is provided with a gear I1, which meshes with the pinion l8upon a shaft I9. A toothed wheel 20 on the main operating shaft 24engages the said pinion I8 to operate the gear I! and the shaft i. Thetoothed wheel 20 carries a stop pin 62 which engages a fixed stop 83 tolimit the range of light'weakenin'g. The shaft 24 carries at 'the top asetting knob 25 to which a cylinder 21 is operatively coupled by aspring 26 the lowerend ofwhich presses against an inturned flange on asleeve 65. The latter has a tooth 3| adapted to engage in notches 6B ina gear 29, the .hub of which extends upward and carries a dial ring 28.

The sleeve. 65 which'surrounds the spring 26 is connected to an outerscale ring 36 by pins 61 which slide in slots 68 in the cylinder 21 asshown. The said gear 29 which rotates freely on the main shaft 24 is nota. complete circle as shown in Fig. 4. It meshes with a smaller gear 30upon a shaft 10 which engages the shutter setting knob 56 by means of acoupling key H in the slot of the knob. The gear 29 carries an abutment32 which is adapted to engage a cam 33 fast on the gear 39. j

The lamp 9 is suitably connected ,to a dry battery 15 as shown in Fig.4. A switch 90 may be used to turn the current on and oil.

The knob 25 carries an index mark 80. cylinder 21 carries a diaphragmscale 8|. ring 36 cai'ries a Scheiner scale 82. The

The The dial From the latter the united rays pass/ ring 28 carries ashutter scale 83. The ring 28 84 and upon the casing ,4

there is a fixed index" also has anindex mark of the exposure meter mark85.

The exposure meter is attached to the camera by pushing the foot 59 intothe recess 58 and the coupiingkey 1'| engages at the same time s theshutter setting knob 56. The exposure meter may now be used to'ascertainthe diaphragm opening which is required for a particular exposure or-itmay be used to ascertain the exposure which is required for use with aparticular predetermined diaphragm opening, all dependnature of theobject, the light con- 1 of. photographic picture ing upon the ditionsand the kind wanted.

As soon as the exposure meter is attached to the camera, it is set toaccord with the Sc'heiner scale of the'filmr This is done as followstached from anotch 66, and by rotation of the ring 36 the'Scheiner indexin scale 82 set oppo-jsite the-Scheiner index mark 84 on the dial ring28 which stands still.

cylinder 65 down,

, other notch 66 aswill be understood. 1

Assuming now that the photographer hasdecided upon cumstancesf andwishes to. ascertain the corresponding correct diaphragm opening. Hethen firstsets the exposure scale value inscale 83 opposite thefixedmark 85. 'I'his he may do by taking hold of thecy'linder 21 which iscoupled to the dial ring 28 by means of the inner cylinder 65andthenrotates cylinder21 and the ring to bring the predeterminedexposure value number opposite the mark 85. During this operation caremust be taken that cylinder 21 is' not depressed against the pressure ofthe spring 26; The setting of the, exposure scale may alsobe'accomplished by rotating the shutter setting knob '56 whichis coupledto the dial ring 28' by shaft 1|] and gears 30 and 29. This settingoperation has of course included a certainsmall movement of the diskwedges 2 and 3 which rotate when dial ring 28 and shaft 24 is rotated asdescribed.

The photographer now looks into the ocular 5,- presses down uponcylinder 21 whereby to' release the knob25 sothat the latter may beseized and rotated to operate the shaft 24 and through theaforesaid'instrumentality rotate the disk wedges 2 and 3 until the lightrays from the lamp and fromvthe object coincide in intensity. Then thecylinder 21 is released and then the index mark 80 on the knob 25 willnow be'oppo'site acertain number on the diaphragm opening scale 8|. Thecamera 'diaphragm is setaccordingly vand the picture is taken with thecorrect'diaphragm opening forthe exposure decided upon."

If on the other hand the photographer has decided upon the diaphragmopening and seeks the exposure value then the operation is as follows.The cylinder 21 is depressed and'rotated until the predetermineddiaphragm opening. number in scale 8| isfset opposite the index mark 80on the knob 25 which stands still. Then the cylinder 21 is released. Thephotographer then again looks into the ocular and a s otat s the yl- Thering 36 and sleeve 65 .is lifted against the pressure. of the spring 26,the tooth 3| being thereby de- Then the ring 36 is re- 1 leased and thespring 26 will move it and the the tooth 3| engaging in anthe exposurerequired under the cirinterposed between said inder 21. This in turncauses rotation of the shaft 24 to operate the disk wedges 2 and 3 andalso causes rotation of the dial ring 28. When the light seen in theocular appears of even intensity, rotation is stopped and the correctexposure value in the scale 83 on dial ring 28 will now be foundopposite the index mark shutter setting knob 56 hasbeen rotated by meansof the gears 29 and30 and by the shaft and the coupling key 1|, so thatthe shutter is adjusted to the correct, exposure .value.

By very dark ob ects it' is not-always possible diaphragm opening is 1.5and the exposure is 1 second, these values being selected for purposesof illustrating the limit of automatic shutter operation of the camera.When :this limit has been reached the shutter setting knob 56 can rotateno furtherand the twogears 30 mesh and locked against further rotationby the engagement of theabutment 32 withinthe -cam 33. The shutter isoperated under according to the exposure value which now appears in thescale 83-opposite the index mark 85. At thistime therefore,'theoperative limit of the shutter having been reached, beenautomatically-operatively uncoupled from the shutter and the latter isno longenoperated automaticaily'inthe ordinary manneraas when timeexposure is used. H f I, claim:

85. Simultaneous the and 29 are out of .to obtain lightroincidence, forinstance if the timeexposure V 5.1 the exposure has I 1. Ainexposuremeter including an electric lampas-a light contrasting measuringelement,

an ocular, an objective and a plurality of prisms including a partlysilvered surface interposed befinder, other prisms tral wedges tosimultaneously weaken the light rays from the lamp v and to. an equalextent strengthen the light rays fror n the objective and vice versadepending upon their direction of rotation, said neutral wedges being ofvariable density in oppositesenses.- s

2.An exposure meter according to claim 1 characterized by that the firstneutralv wedge is located adjacent to the entrance pupil of the bundleof light rays from the objective and the I second neutralwedge 18located adjacenttothe entrance pupil of the bundle of light rays fromthe lamp.

3. Anexposure meter according to claim 1 wherein said means comprisesashaft for supporting and rotating the disk formed neutral wedgesandmechanism for operating said shaft to simultaneously weaken the lightrays from the lamp and to anequal extent strengthen the light rays fromthe objective and vice versa depending upon their direction of rotation.

IW'ILLY scrmrnn.

